The present invention relates to a wind turbine with a rotor hub and at least one rotor-blade connected to a pivot-bearing. By at least one electrical, pneumatic and/or hydraulic actuator, each rotor-blade can be rotated on its longitudinal axis and can be held in a defined position by means of a brake, whereat the brake is connected to the actuator. There is at least one gear box connected to the actuator, which rotates on a pivot-bearing. The pivot-bearing comprises an inner and outer ring, wherein one ring is screwed onto the hub and the other one connects the rotor blade. By rotating the ring, to which the blade is mounted on, the rotor blade can be rotated in its longitudinal axis. This ring may be the outer or the inner ring of the bearing. In order to limit the energy caused by the wind in case of an emergency, or to interrupt or reduce the energy generation, the rotor blade is turned into the position in which a lower amount of wind power is absorbed by the rotor. In order for each blade to be provided with a self-sufficient rotation about its longitudinal axis, even on failure of the mains supply, each drive has one or more independent energy storages, which in case of an emergency, provide one or more rotor blade drives (actuators) on each rotor blade, with energy and release one or more holding brakes.
The rotor blade pitching of a wind turbine is used for speed control (power control) of the turbine at the range of nominal power, and also as an aerodynamic braking system. Therefore each rotor blade has one or more actuators. To achieve this with the pitch system, it is rotated to an angle between vane position and working position, and with the system using the principle of active-stall into the opposite direction to stall.
In case of a failure it is advantageous to turn all rotor blades into the position with a low power generation if possible. A version of existing systems for rotor blade pitch comprises one or more electric drive-modules for each rotor blade, including one or more connected actuators, which are equipped with one or more holding brakes to keep the position. This allows for each blade to be pitched and held at position individually. However, nearly at all known actuators, the holding brakes of rotor blades are designed so that the disconnection of the brake control leads to the blocking of the actuator shaft and thus there is the risk that the blade-pitch cannot or can only be performed insufficiently, if, for example, a cable-connection to a brake has been interrupted. Especially in the case that an actuator does not deliver any torque, the corresponding rotor blade stays in its maximum working position. In a system working with active brakes, there is the disadvantage that they cannot keep the rotor blade from rotating into the direction in which a further rotation of the rotor takes place, in the event that the actuation of the brake-coils is not possible.
Consequently a malfunction of the rotor blade pitch-drive can cause a critical situation for the entire wind turbine. In particular, exceeding the permissible rotor speed can cause danger to people or a substantial or total damage to the wind turbine.
According to the state of the art technology, brakes used in the drive-train for pitch-drives are executed in such a way, that the brake-coil with friction lining is fixed, for example to the motor housing, and the brake-hub is rotating together with the motor shaft, and thus a closing of the brake consequently stops the motor shaft and the associated gear and rotor-blade. However, one or more brakes on an actuator system for the rotor-blades, may as well be, for example connected between the motor and gearbox or via geared-belt-drive to the rotor-blade.
The WO 99/23384 describes an apparatus for adjusting of rotor-blades at a rotor-hub of a wind turbine, which has a drive for rotating the rotor-blades. The rotor-blade adjustment can also be used as a braking system for shutdown of the wind turbine by turning the rotor-blades towards vane position, and so reducing the power, respectively speed, of the wind turbine. In order to ensure the slow-down of the wind turbine by the pitch-system, even in the event of a power loss, a switchable return stop is connected to the rotor blades, to block the motor-shaft which prevents the rotor blades to turn from vane position into working-position. The return stop is deactivated during failure-free operation and is automatically activated at failure of power supply, which causes the blades to only be able to turn into vane position and be kept there.
In the document EP 1 763 126 B1 a device for controlling the blade angle of a rotor-blade of a wind turbine is described, wherein the device contains the following components: a pitch control system with a power converter, a DC voltage circuit with capacitor for power supply to the pitch control system, an AC power source for energy supply to the DC voltage circuit and an alternative buffer battery for power supply to the control system in case of AC power failure.
The different versions of these suggestions have significant negative impacts, such as e.g. the system with switchable freewheel has the disadvantage that the full motor-torque has to be blocked, causing a rigorous blocking in one direction and that it requires an additional coupling for activation, or an auxiliary power supply. The systems using a passive brake do not feature a redundant emergency method respectively do not describe a truly redundant emergency apparatus, in case of an error at the actuator system, e.g. damaged actuator, or when a brake fails to release.
The object of this invention is to provide an additional device, means a “redundant emergency apparatus for each rotor blade”, in the event that one or more standard emergency devices because of a failure, do not adjust the pitch-angle of one or more rotor-blades into a position of power limitation.
These problems shall be solved in the way that each available brake is opened or is kept open, as soon as a torque on the rotor-blades longitudinal axis attempts to rotate the rotor-blade in the direction of a decreasing driving torque for the rotor, and in the case of a torque trying to move the rotor-blade into the maximum working position, this rotary movement shall be stopped already at the beginning, anyhow an adjustment to the aerodynamic braking position (vane position) is carried out for the corresponding rotor-blade.